I was driving down the highway today, in fifth, around 60 or so, and heard a loud pop from the passenger side. A few miles down the road it occurred once more, but I didn't hear it at all after, not even on the way back.
I inspected the undercarriage briefly, and all I saw was a bit of oil dripping from someplace, (which is fairly normal.

) but the oil was hitting the exhaust pipe.
Any helpful thoughts on unusual popping sounds from under the car?